A review of geomorphic processes and landforms in the Dry Valleys of southern Victoria Land: implications for evaluating climate change and ice-sheet stability

The Dry Valleys are subdivided into three microclimate zones on the basis of summertime measurements of atmospheric temperature, soil moisture, relative humidity and wind-speed/ direction. Subtle variations in these climate parameters result in considerable differences in process geomorphology and in the development of unique landforms within each zone. The mapped zones include a coastal thaw zone, an inland mixed zone and a stable upland zone. Landforms within each zone are subdivided into macroscale features (e.g. valleys, slopes and gullies), mesoscale features (e.g. polygons and viscous-flow features) and microscale features (e.g. rock and near-surface soil features, including the effects of salt weathering, wind erosion and pitting). We present a review of landscape development in the Dry Valleys with implications for long-term climate change and icesheet stability. Chronological control is afforded by Ar/Ar dating of volcanic ash-fall deposits and cosmogenic nuclide analyses of surface boulders. Collectively, the data call for persistent cold and dry conditions in the stable upland zone for approximately the last 14 Ma, although some level of climatic amelioration and landform modification may have occurred within low-lying regions and in the inland mixed zone. Landscapes represent the physical manifestation of several interrelated processes, including variations in tectonism, lithology and climate. Of these, climate is known to change on timescales relevant to human endeavours and, thus, changing landscapes are commonly viewed as resulting from a change in local climate conditions. Important climate parameters include variations in temperature, rainfall, wind velocity and solar radiation. Notwithstanding the importance of tectonic structure and lithology in shaping landscapes, especially in areas of active tectonics, climate parameters yield diverse geomorphic processes, which in turn produce distinct assemblages of landforms. Among climate parameters, the leading driver of landscape change is the abundance, and state, of water. For example, in comparing arid and humid temperate environments, arid landscapes show far less waterrelated fluvial activity than humid environments. Climate zones characterized by mean annual temperatures at or below the freezing point of water will also have relatively little influence from fluvial activity. Rather, periglacial and glacial processes will prevail, and the landforms will be formed and modified by freeze–thaw cycles and the movement of ice. These relationships offer a powerful tool for defining climate zones, understanding how they form and evolve, and even for predicting the nature of landforms under different climate conditions. Exploiting such linkages among climate and landscape has led naturally to the notion of morphogenetic zones, with each zone containing a distinctive landform assemblage that corresponds with major climatic belts. In this paper, we use the terms equilibrium landform and equilibrium landform assemblages to describe landforms produced in balance with local microclimate conditions in the Dry Valleys. Although the concept is similar to that of morphogenetic zones, we prefer the phrase equilibrium landform assemblage because it highlights the importance of very small microclimate variations within the Dry Valleys that yield disproportionally large changes in geomorphic process and resulting landscapes. In the absence of buffering vegetation and biological processes, the Dry Valleys landscape is extremely sensitive to minor climate variation. The location of the zero-degree summer isotherm is one of the most critical geomorphic thresholds impacting landscape evolution in the Dry Valleys region, and, indeed, in most high-latitude environments and polar deserts worldwide. From: Hambrey, M. J., Barker, P. F., Barrett, P. J., Bowman, V., Davies, B., Smellie, J. L. & Tranter, M. (eds) Antarctic Palaeoenvironments and Earth-Surface Processes. Geological Society, London, Special Publications, 381, http://dx.doi.org/10.1144/SP381.10 # The Geological Society of London 2013. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics by guest on July 2, 2013 http://sp.lyellcollection.org/ Downloaded from